181.
The limiting position of the point of intersection of the lines $$3x+4y=1$$ and $$\left( {1 + c} \right)x + 3{c^2}y = 2$$ as $$c$$ tends to 1 is :
182.
The parametric equation of a line is given by $$x = - 2 + \frac{r}{{\sqrt {10} }}$$ and $$y = 1 + 3\frac{r}{{\sqrt {10} }}.$$ Then, for the line :
A
intercept on the $$x$$-axis $$ = \frac{7}{3}$$
B
intercept on the $$y$$-axis $$ = - 7$$
C
slope of the line $$ = {\tan ^{ - 1}}\frac{1}{3}$$
The cartesian equation is $$x + 2 = \frac{{y - 1}}{3},\,{\text{i}}{\text{.e}}{\text{.}},\,3x - y + 7 = 0.$$
183.
Let $$0 < \alpha < \frac{\pi }{2}$$ be a fixed angle. If $$P\left( {\cos \,\theta ,\,\sin \,\theta } \right)$$ and $$Q\left( {\cos \left( {\alpha - \theta } \right),\,\sin \left( {\alpha - \theta } \right)} \right),$$ then $$Q$$ is obtained from $$P$$ by the :
A
clockwise rotation around the origin through an angle $$\alpha $$
B
anticlockwise rotation around the origin through an angle $$\alpha $$
C
reflection in the line through the origin with slope $$\tan \,\alpha $$
D
reflection in the line through the origin with slope $$\tan \left( {\frac{\alpha }{2}} \right)$$
Answer :
reflection in the line through the origin with slope $$\tan \left( {\frac{\alpha }{2}} \right)$$
Clearly, $$OP = OQ = 1$$ and $$\angle QOP = \alpha - \theta - \theta = \alpha - 2\theta $$
The bisector of $$\angle QOP$$ will be perpendicular to $$PQ$$ and also bisect it. Hence, $$Q$$ is the reflection of $$P$$ in the line $$OM$$ which makes an angle equal to $$\angle MOP + \angle POX$$ with the $$x$$-axis, i.e., $$\frac{1}{2}\left( {\alpha - 2\theta } \right) + \theta = \frac{\alpha }{2}$$
So that slope of $$OM$$ is $$\tan \left( {\frac{\alpha }{2}} \right).$$
184.
The equation of straight line passing through $$\left( { - a,\,0} \right)$$ and making a triangle with the axes of area $$T$$ is :
If the line cuts off the axes at $$A$$ and $$B,$$ then the area of triangle is
$$\eqalign{
& \frac{1}{2} \times OA \times OB = T \cr
& {\text{or }}\frac{1}{2} \times a \times OB = T \cr
& {\text{or }}OB = \frac{{2T}}{a} \cr} $$
Hence, the equation of line is $$\frac{x}{{ - a}} + \frac{y}{{\frac{{2T}}{a}}} = 1\,\,{\text{or }}2Tx - {a^2}y + 2aT = 0$$
185.
What is the acute angle between the lines represented by the equations $$y - \sqrt 3 x - 5 = 0$$ and $$\sqrt 3 y - x + 6 = 0\,?$$
The equation of the graph is $$y = \cos \,x.\cos \left( {x + 2} \right) - {\cos ^2}\left( {x + 1} \right)$$
$$\eqalign{
& {\text{or, }}y = \frac{1}{2}\left\{ {\cos \,2 + \cos \,2\left( {x + 1} \right)} \right\} - \frac{1}{2}\left\{ {1 + \cos \,2\left( {x + 1} \right)} \right\} \cr
& = \frac{1}{2}\left( {\cos \,2 - 1} \right) \cr
& = - \frac{1}{2}.2{\sin ^2}1 \cr
& = - {\sin ^2}1 \cr} $$
The graph is parallel to the $$x$$-axis, and $$\left( {\frac{\pi }{2},{\mkern 1mu} - {{\sin }^2}1} \right)$$ satisfies it.
187.
Let $$P = \,\left( { - 1,\,0} \right),\,Q = \left( {0,\,0} \right)$$ and $$R = \left( {3,\,3\sqrt 3 } \right)$$ be three point. The equation of the bisector of the angle $$PQR$$ is-